Who used to negotiate contracts for you? Surely they aren't throwing you in blind to do this unassisted your first time. Simple realistic goal for your endpoint should be whatever your previous rate for things was + annualized bump for inflation (overall or healthcare inflation specifically).
As for having all the information, they don't have it all. They have your previous case and procedure data, but you can likely know future directions for your practice that they cannot predict as accurately. Maybe give them a little discount on something that used to be worthwhile if they will give you a bump in an area that will be growing.